A data center typically contains information technology (IT) equipment like servers, telecom equipment, networking equipment, switches and other IT equipment arranged in racks or frames. The heat generated by such IT components is cooled with the help of cooling units. Typically, the cooling units are computer room air conditioners (CRAC) or computer room air handlers (CRAH) which supply cold air or air draft to cool the heat generated. More recently advanced cooling units such as in-row coolers, rear door coolers, liquid cooled cabinets and chip cooling techniques have come into practice.
Data centers have now become energy guzzlers. With the drastic increase in energy prices, the huge energy bill is one of the major concerns for the data center managers. Power consumed by cooling equipment contributes to a major portion of the total data center power consumption. The main challenge is to ensure safety of IT equipment by ensuring appropriate temperatures in the data center and at the same time ensuring efficient cooling efficiency of the data center. Due to poor design of the data center, data center mangers face lot of problems like hot spots, low tile flow rates etc. General measures taken are to decrease supply temperature of cooling units, increase cooling capacity near the problem area etc. These measures lead to decrease in cooling efficiency. Hot spots and low cooling efficiency are the major challenges faced by data center managers in thermal management of data centers.
Owing to the challenges stated above, various attempts have been made to design and operate new data centers efficiently. Efficient design of data center include proper arrangement of racks, tiles, CRACs etc, adequate plenum depth, use of airflow management techniques such as aisle containment etc. Efficient control schemes have been developed to control parameters of CRAC like supply temperature, supply flow rate or tile flow rates in accordance to changes in heat generation, temperature, pressure and airflows in the data center. These control schemes make CRAC run at efficient possible efficiency while maintaining satisfactory temperatures in the data center at the same time. Different algorithms for workload placements have been developed which take cooling related parameters like recirculation, CRAC capacities into account while executing placement requests. Numerical models such as computational fluid dynamic (CFD) models as well as data based models using neural networks are being used to facilitate efficient control schemes.
The attempts towards efficient designing of new data center aim at exploration of efficient design and operation parameters pertaining to fully occupied data center. However, the new data centers seldom are occupied within short time. The time of ramping up of a new data center ranges from few months to few years depending upon financial constraints, business constraints, resources availability etc. In some cases, the data center may never be completely occupied for many years because it is designed for expected future needs. The data center operates at inefficient conditions during this time of ramping up of data center as its efficient possible efficiency is ensured only for the full occupancy. Hence, there is a need for a method for maintaining PUE of a data center constant/within narrow range during ramping up.